Upvote:3
The following info is from Timatic, the database used by airlines:
For Belgrade:
VISA NOT REQUIRED
For Abu Dhabi:
VISA NOT REQUIRED
For Sri Lanka:
Visa required, except for Nationals of Bulgaria can obtain a visa on arrival for a maximum stay of 30 days.
So, your wife needs no visas at all.
For Belgrade:
Visa required, except for holders of confirmed onward tickets for a max. transit time of 24 hours
(you can even leave the airport and visit Belgrade, by presenting your passport and German residence permit)
For Abu Dhabi:
Visa required, except for Holders of confirmed onward tickets for a max. transit time of 24 hours
For Sri Lanka:
VISA NOT REQUIRED
So you need no visas at all.